Blender cycles glass from sideview not transparent at all
Your normals are facing the wrong way - press Ctrl-N in edit mode (with everything selected) to recalculate them.

How they were before (wrong):



After recalculating:



The reason the glass looks bad with inverted normals is because glass uses a fresnel function to calculate where the most reflections should be:





(both spheres use exactly the same material)